THOUSANDS of pregnant women may be unwittingly putting their unborn children at risk of serious illness and deformity, according to new research published this morning.

THOUSANDS of pregnant women may be unwittingly putting their unborn children at risk of serious illness and deformity, according to new research published this morning.

The study indicates that those born before 1988 may be inadequately protected against rubella, because they were not given a double dose of vaccine against the virus.

Scientists in Japan recorded 31 cases of birth defects caused by rubella in women who contracted the disease despite being vaccinated as children.

In Britain, the measles mumps rubella (MMR) vaccination regime, which involves two pre-school doses, was only introduced in 1988. Before then, women born in the UK were only given one rubella jab in their early teens.

Rubella, also known as German measles, causes a fairly trivial illness in children but can be devastating if it affects a woman in the early months of pregnancy.

There is a chance the virus will infect the foetus and cause a range of severe birth defects, known as rubella syndrome.

The risk facing women who have had only one rubella jab was highlighted today in Chemistry & Industry magazine.

Researcher Shigetaka Katow, who works with the US Centres for Disease Control and Prevention, said, "Women who have had only one injection may not be properly protected."

The findings highlight a further danger of boycotting the MMR jab.

Children who are not vaccinated with MMR could give their pregnant mothers the virus, said Katow. Those who did not give their sons and daughters the MMR jab may be endangering their own unborn children.

Falling rates of MMR vaccinations in the UK meant the risk of pregnant women coming into contact with the virus was increasing.

Childhood immunisation rates have fallen alarmingly because of fears - refuted by the Department of Health and leading experts - of a possible link between the MMR jab and autism.

Some parents are reverting to single-vaccine jabs. But most are focusing on measles, which is perceived as posing the greatest threat.

The new research suggests that unless children are given two doses of the single rubella vaccine they may not be adequately protected.

Cases studied by the Japanese researchers included a 34-year-old pregnant woman who contracted rubella from one of her own children.

She had been vaccinated at the age of 14, but still carried the virus. It was believed she caught the infection from her second child, who had not been vaccinated and was diagnosed with rubella.

When the woman's third child was born, he had difficulty breathing and showed signs of infection. He had an odd facial appearance, clouded corneas, a squint and cataracts.

Blood tests confirmed congenital rubella syndrome.

A Department of Health spokeswoman said GPs were supposed to screen women of child-bearing age for immunity to rubella.

"It is up to the GP to screen anyone who is thinking of starting a family for protection," she said.

But Chemistry & Industry said information about rubella screening was only available on an obscure part of the DoH website, www.doh .gov.uk/greenbook.

Ms Lucas added, "No vaccine is perfect. There is always the possibility for vaccine failure, and we have on rare occasions seen rubella infections in women who had previously been immunised. But rubella vaccination is extremely effective."

Nevertheless, the Department of Health recommended two doses which ensured "extremely high levels of protection".